Not a subject for every dinner table, but worth knowing in case you should be unlucky enough to get a blocked drain or a flood. At least the London Assembly knows which way the drains flow... The London assembly have released a draft document for sustainable urban drainage (SUDS) which contains this image of the main sewer network of London:

This plan shows a small fraction of London's invisible underground architecture, the scale it is plotted at reveals the geomorphology underlying this most urban of infrastructural developments.

The Royal Horticultural Society (RHS) is unveiling plans to create a stunning new 156 acre RHS Garden in the heart of the North West by bringing back to life the lost historic grounds at Worsley New Hall in Salford. The site forms part of the 3rd Duke of Bridgewater’s estate and adjoins the Bridgewater Canal in Worsley, Salford. RHS Garden Bridgewater is planned to open in 2019 as part of the RHS’ wider ten year £100+ million investment programme to achieve its Vision to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.RHS gets a new gardenRHS unveils new 156 acre garden in Salford.

August brings in the first period of relative calm in my season's calendar. The catching up is over, the hedges are cut, the meadows are down and cleared, the herbaceous border is doing its thing, and the lawns have slowed down at long last. While the soil surface remains dry the second flush of weed seedlings hold back from germinating. And many of us are on holiday. But the gardens can seem a bit adrift between the glories of the June borders and the early autumn lightshow - a bit of a lull.

This year the Hydrangea aspera 'Villosa' is making an early entrance. For some reason waning in popularity (at least nurseries don't seem to be growing it as much as previously), this hard working gem is starting to glow. The grey foliage makes a fine foil for the rosy-lavender lacecap flower heads. It associates well with Cotinus coggyria 'Royal Purple', white japanese anemones, and Hemerocallis. Here it is growing through a prostrate juniper on one side, and - not visible here - on the other a bed of Mahonia aquifolium grown as ground cover, and has formed its characteristic loose hummock shape. It requires no pruning or fiddling with, tolerates most soils and sun or light shade, flowers reliably, and doesn't suffer from pests or diseases. If it has a fault it is that (in common with many of its genus) it looks a bit woeful after the first frosts with the leaves hanging like wet tissues from the stems.

Another mid-summer beauty is Acidanthera bicolor, maybe now known as Gladiolus murielae, the Abyssinian Gladiolus, a prettily scented plant growing on lanky stems to 70cm or more in height. Not reliably hardy outside sheltered spots in the South East, but if planted deep and well mulched it should survive some testing weather, or may be lifted and stored like regular gladiolus corms. Not a temperamental plant, it makes do in any reasonably drained soil as long as it sees the sun, and is kept from strong winds which will knock it over. The corms bulk up very fast, and it flowers solidly for many weeks through to late September.

A newish disease of uncertain provenance, it causes limb lesions and eventual limb shedding with obvious potential for harm to the public. The identifying lesions are on the upper surface of the limbs and thus near impossible to spot from the ground, but at least it is usually smaller limbs that are affected first. These are still up to 10cm diameter and thus physically substantial, and the disease can in time affect limbs up to 1 ft in diameter. Pruning out affected branches is the only current control.

The fungus (Splanchnonema platani) has been found on Planes in Europe for a long time where it is regarded as a minor problem, and has also been found in the UK as one of a population of saprophytic and parasitic fungi present in affected wood, but has not produced spores here until 2013, and it is not clear why it has now started. Research continues.

If you have Planes in your garden that might pose a danger to yourself or others then it makes sense to have them aerially inspected every 4-6 months if possible, as the disease apparently can develop this fast. For those with trees overhanging public spaces it is advisable to notify your insurers of this risk.